Simultaneous determination and pharmacokinetic characterization of 4-methyl-N-ethylcathinone and its metabolites in rat whole blood using a LC-MS/MS method.

4-Methyl-N-ethylcathinone (4-MEC) is a novel psychoactive substance and its in vivo exposure characterization remains unknown. In this study, a sensitive and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and fully validated for the simultaneous quantification of 4-MEC and its two major metabolites in rat whole blood. Then it was applied to pharmacokinetic studies of 4-MEC in rats by intravenous and intragastric administration, characterizing the concentration-time profiles of the parent compound and its metabolites. The results revealed distinct exposure patterns between 4-MEC and its metabolites. Notably, M2 (N-deethylated metabolite) exhibited a prolonged detection window compared with 4-MEC, supporting metabolite-based monitoring strategies and thereby extending its application in forensic toxicology and drug abuse identification.